Mitochondrial RNA polymerase is a critical mediator of LPS-induced inflammatory responses and septic shock.

Sepsis, particularly septic shock, is a life-threatening condition driven by a dysregulated inflammatory response. Mitochondria are vital for orchestrating the LPS (lipopolysaccharide)-induced innate immune response. At the core of mitochondrial functionality lies mitochondrial RNA Polymerase (POLRMT). This study delineates POLRMT's functional role and underlying mechanisms in LPS-induced pro-inflammatory responses across various macrophage models and in vivo. Through multiple genetic strategies, including stable shRNA-mediated knockdown and CRISPR/Cas9-mediated ablation, we demonstrated that POLRMT deficiency in THP-1 human macrophages, peripheral blood mononuclear cells (PBMCs), and murine bone marrow-derived macrophages (BMDMs) consistently attenuated LPS-induced transcriptional upregulation and secretion of key pro-inflammatory cytokines (IL-1β, TNF-α, IL-6). Conversely, POLRMT overexpression in THP-1 cells augmented these inflammatory responses. LPS-induced enhancements in mitochondrial Complex I activity and ATP content, alongside NFκB activation, were dependent on POLRMT expression. Genetic perturbation of POLRMT directly correlated with altered mitochondrial function and NFκB activity. Pharmacological inhibition of POLRMT with a specific inhibitor IMT1 also suppressed LPS-induced cytokine production, mitochondrial activation, and NFκB activity in vitro. The in vivo studies revealed that knockdown of POLRMT in CD68-expressing cells protected mice from LPS-induced septic shock, reducing mortality and systemic cytokine levels. Oral administration of IMT1 similarly conferred protection against septic shock, correlating with diminished circulating pro-inflammatory cytokines and reduced NFκB activity in murine PBMCs. Collectively, these findings establish POLRMT as a mediator of LPS-induced inflammatory responses in macrophages/monocytes.